# When is transform width in code not equal to the transform width in inspector?

I've come across a strange case in Unity's UI where the width of a RectTransform isn't the same as what is being reported. I have a transform which is 50 by 50 with no scaling, it is a root object of the canvas yet when I use the information that I get from the transform in code to draw from the bottom left edge of the transform to the top right it doesn't reach all the way!

Gizmos.color = Color.red;
Vector2 pos = new Vector2(transform.position.x, transform.position.y);
Gizmos.DrawLine(pos - transform.sizeDelta, pos + transform.sizeDelta);

Vector3[] corners = new Vector3[4];
transform.GetWorldCorners(corners);

Gizmos.color = Color.magenta;
Gizmos.DrawLine(corners[3], corners[0]);
Gizmos.DrawLine(corners[0], corners[1]);
Gizmos.DrawLine(corners[1], corners[2]);
Gizmos.DrawLine(corners[2], corners[3]);


The first section should draw a line from the bottom left to the top right according to what the transform reports are the width and height however they don't reach across the entire transform. Using GetWorldCorners the actual corners can be found and drawn around, with that data you can extract that the actual width is 60 (150.2 - 30.2 = 120 / 2 = 60)!

Why? Is this a bug or an I missing something obvious here?